> Jared, thanks for the pointer!>> As it turns out - if I rename sqlnet.ora file to _sqlnet.ora to make it> "dissapear" - the problem is gone and I can do "sqlplus '/ as sysdba'"!?>> With sqlnet.ora present (btw it was created by the 'netca'), it does not> matter if SLNET.AUTHENTICATION_SERVICES is NTS or NONE, ORA-01031 would> follow any attempt at '/ as sysdba'.>

Setting it to NONE will also cause the error.

It isn't necessary to rename the sqlnet.ora file, just remove the
sqlnet.authentication_services
line from the file.

I just checked few of my other Linux (4) systems (32 and 64 bit) and none of
> them had sqlnet.ora file (I installed these quite some time ago, and never> noticed that sqlnet.ora is not there from day 1), how strange...>

Oracle will use the tnsnames.ora that is present even without sqlnet.ora.

It will also use LDAP via OID autodiscovery without a sqlnet.ora file.
That requires 10g+ and some setup by the network admin however.